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Magnetic anisotropy and X- ray diffraction study of clay minerals in the decollement horizons of the western Helvetic nappes, SW Switzerland

Published online by Cambridge University Press:  09 July 2018

P. Dick  and
M. Burkhard
P. Dick*
Affiliation:
Institut de Géologie, rue E. Argand 11, CH-2007 Neuchâtel, Switzerland
M. Burkhard
Affiliation:
Institut de Géologie, rue E. Argand 11, CH-2007 Neuchâtel, Switzerland
*
*E-mail: [email protected]
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Abstract

Anisotropy of magnetic susceptibility (AMS) and X-ray diffraction studies on shale decollement horizons in the Western Helvetic nappes were conducted to delineate the interactions between clay particles and deformation during a non-coaxial thrusting deformation. The reorientation of magnetic lineations in the decollement horizons, from a NW—SW thrusting direction to a NE—SW oriented lateral escape, provides the opportunity to study the evolution of magnetic fabrics and clay mineralogy during a two-step deformation history. The AMS of these shales originates from paramagnetic phyllosilicate minerals: illite, phengite and chlorite. Clay mineral studies indicate that magnetic lineations parallel to the thrust directions correspond to the spatial organization of the basal planes of phengites, whereas those parallel to the lateral escape movement are caused by illites. This work indicates that the change in direction of magnetic lineations from orogenic contraction to lateral escape not only records the strain history but also the dissolution and neoformation of paramagnetic minerals.

Keywords

magnetic anisotropyX-ray diffractionHelvetic nappesSwitzerland
Type
Research Article
Information
Clay Minerals , Volume 36 , Issue 2 , June 2001 , pp. 181 - 196
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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